Fix UnsupportedOperationException

SpigotCore_Main/src/de/steamwar/command/SWCommand.java

@@ -162,7 +162,7 @@ public abstract class SWCommand {
     }
 
     private List<Method> methods() {
-        List<Method> methods = Arrays.asList(getClass().getDeclaredMethods());
+        List<Method> methods = new ArrayList<>(Arrays.asList(getClass().getDeclaredMethods()));
         methods.addAll(Arrays.asList(SWCommand.class.getDeclaredMethods()));
         return methods;
     }